Sondland testified that he told a top aide to Ukrainian President Volodymyr Zelenskiy that the United States was going to withhold military assistance unless Ukraine launched investigations into the 2016 presidential election and alleged corruption by Joe Biden and his son Hunter.

"I now recall speaking individually with Mr. (Andriy) Yermak, where I said resumption of U.S. aid would likely not occur until Ukraine provided the public anti-corruption statement that we had been discussing for many weeks," Sondland said.

Sondland said he had forgotten about the conversation when he testified to House investigators in October. He told members of Congress that he remembered his conversation with Yermak after he reviewed the opening statements from Bill Taylor, the acting ambassador to Ukraine, and Tim Morrison, a former adviser to Trump on Russian and European affairs.

Volker told Congress that Ukrainian officials asked to be connected with Rudy Giulianibecause they believed he had a direct line to President Donald Trump. He claimed that he did not know of any "quid pro quo" tying U.S. military aid to investigations into the Bidens or the 2016 presidential election.

"You asked what conversations did I have about that quid pro quo, et cetera," Volker said. "None, because I didn't know that there was a quid pro quo."